JP2680484B2 - Optical writing type liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing type liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices are generally used as displays for portable personal computers and the like, taking advantage of their small size and low power consumption, and their popularity has been remarkable in recent years. On the other hand,
Not only as a display, but also research and development for other uses are being actively conducted. For example, an optical writing type liquid crystal display device (hereinafter, abbreviated as an optical writing type LCD) is one of them.

Whereas the conventional liquid crystal display device was a device for converting an electric signal into a visible image, an optical writing type LCD
Is a so-called light-to-light conversion device, and when combined with a projection optical system, a light amplification function of enlarging and projecting image information by laser light or CRT (cathode ray tube) as a bright image on the screen, and red image information. Has a wavelength conversion function such as converting to blue image information.

This photo-writing LCD is provided with two glass substrates having transparent electrodes, a photoconductive film made of amorphous silicon, a light shielding layer, a dielectric mirror and a liquid crystal layer. The conductive film, the light-shielding layer, the dielectric mirror, and the liquid crystal layer are sandwiched, which is a so-called sandwich.

In the photo-writing type LCD having such a structure, the impedance ZPC of the photoconductive film is larger than the impedance ZLC of the liquid crystal in the dark state where no light is irradiated, and therefore the photoconductive film is larger than the liquid crystal layer. It takes voltage. When light is irradiated from the side of the photoconductive film, the impedance ZPC of the photoconductive film is lowered and ZPC <ZLC is established, so that a voltage is applied to the liquid crystal layer. At this time, the light emitted from the side of the liquid crystal layer, depending on the voltage applied to the liquid crystal layer,
That is, it is modulated according to the intensity of the light applied to the photoconductive film.

Further, the display mode of the liquid crystal is J. Grinberg et.
As shown in al.opt. eng. 14,217 (1975), since a bright display is possible, the twist angle is 45 °.
The twisted nematic type of has been used.

[0007]

In such a conventional photo-writing type LCD, a sufficient voltage is applied to the liquid crystal because the ratio of the voltage actually applied to the liquid crystal layer during light irradiation and in the dark state is small. There is a problem that the display becomes dark without being applied.

An object of the present invention is to provide an optical writing type LCD capable of improving the display brightness.

[0009]

A light writing type liquid crystal display device having two liquid crystal cells of twist nematic type, wherein the two liquid crystal cells have a twist angle of 45 °.
Liquid crystal cell in which twisting is in the opposite direction and voltage is applied
The product of the birefringence of the liquid crystal enclosed in and the thickness of the liquid crystal layer.
nd is between 0.45 and 0.75 and the incident polarization axis is on the light incident side.
Direction opposite to the twist direction of the liquid crystal with respect to the liquid crystal molecular axis of
It is configured to form an angle of 22.5 ° ± 10 ° .

[0010]

[Action] two liquid crystal cell of the twisted nematic type,
With a twist angle of 45 °, the twist direction is opposite,
Liquid crystal birefringence and liquid crystal enclosed in a liquid crystal cell that applies pressure
The product value Δnd of the crystal layer thickness is between 0.45 and 0.75
The incident polarization axis is aligned with the liquid crystal molecular axis on the light incident side.
Make an angle of 22.5 ° ± 10 ° opposite to the twist direction of
Which is configured as, according to the results of measurement of the relationship between the transmittance of the applied voltage and the incident changed using the device,
The steepness can be improved, that is, the change in transmittance with respect to the change in voltage can be increased. Therefore, when the photo-writing type liquid crystal display device is driven at a certain voltage ratio, the steepness is improved, so that a bright display can be obtained in the ON state.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a sectional view showing the structure of an embodiment of a liquid crystal cell provided in the photo-writing type LCD according to the present invention.

The optical writing type LCD of this embodiment constitutes a so-called compensation type reflection type projection liquid crystal display device in which two twisted nematic type liquid crystal cells are laminated.

As shown in the figure, the photo-writing type LCD of this embodiment has a two-layer liquid crystal cell, that is, a first liquid crystal cell to which a voltage is applied and a second liquid crystal cell for compensation as described later. And are stacked.

The first liquid crystal cell is a transparent glass substrate 11a.
And 11b, transparent electrodes 12a and 12b, an a-Si (amorphous silicon) layer 13, a light shielding layer 14, a dielectric mirror 15, alignment films 16a and 16b, and a sealing member 17, and are formed as follows. .

ITO (indium) is formed on the glass substrate 11a.
A tin oxide) film is formed by the sputtering method to form the transparent electrode 12a. Next, an a-Si layer 13 which is a photoconductor is formed on the transparent electrode 12a by a plasma CVD (Chemical Vapor Deposition) method. Then, a
On the Si layer 13, an acrylic resin in which carbon black is dispersed is applied and baked to form the light shielding layer 14. Then EB
A dielectric mirror 15 is formed by alternately stacking SiO ₂ and TiO ₂ by the vapor deposition method.

The substrate thus formed and the transparent electrode 12b formed by forming the ITO film on the other glass substrate 11b by the sputtering method are coated with polyimide by the spin coating method and baked. Alignment film 16a
And 16b. Next, the surfaces of the alignment films 16a and 16b of these substrates are subjected to an alignment treatment by rubbing, and then bonded together via a seal member 17 including a spacer.

In this way, the first liquid crystal cell is formed.

A liquid crystal is injected and sealed in a space formed by the alignment films 16a and 16b and the seal member 17 to form a liquid crystal layer 18.

The light shielding layer 14 is provided to prevent the a-Si layer 13 which is a photoconductor from being exposed to the strong light (reading light) from the liquid crystal layer 18 side.

An AC power supply 19 is connected to the transparent electrodes 12a and 12b so that a voltage can be applied to the first liquid crystal cell.

The second liquid crystal cell is a transparent glass substrate 21a.
And 21b, the alignment films 22a and 22b, and the seal member 23, and are formed as follows.

Similar to the formation of the first liquid crystal cell, the glass substrates 21a and 21b are coated with polyimide by spin coating and baked to form the alignment films 22a and 22b. Next, the surfaces of the alignment films 22a and 22b on these substrates are subjected to an alignment treatment by rubbing, and then bonded together via a seal member 23 including a spacer.

In the above-mentioned alignment treatment in forming the first and second liquid crystal cells, the twist directions are the same as those of the first liquid crystal cell and the second liquid crystal cell.
The liquid crystal cell and the liquid crystal cell are oppositely oriented.

A liquid crystal layer 24 is formed by injecting and sealing liquid crystal into the space formed by the alignment films 22a and 22b and the seal member 23.

The liquid crystal to be enclosed in the liquid crystal layers 18 and 24 is, for example, SD-4107 (manufactured by Chisso Corporation, Δn = 0.135),
ZLI-1646 (manufactured by Merck & Co., Δn = 0.08) may be used.
Here, Δn is a birefringence index.

FIG. 1 is an explanatory view showing the relationship between the liquid crystal molecule axes of the first and second liquid crystal cells and the incident polarization axis, and FIG.
Shows the rubbing directions of the substrates of the first and second liquid crystal cells, and FIG. 1B shows the positional relationship between the incident polarization axis and the liquid crystal molecular axis.

In the first and second liquid crystal cells, the directions of liquid crystal molecules on the glass substrate on the side in contact with each other are orthogonal to each other.
It has the same refractive index as glass and is adhered and fixed by a transparent resin 25 having an adhesive property.

As the resin 25, for example, resin 801se-f (manufactured by Kyoritsu Chemical Industry Co., Ltd.) may be used.

Therefore, as shown in FIG. 1 (A), the rubbing direction γ ₁₁ of the lower substrate of the first liquid crystal cell (on the alignment film 16b side) and the upper substrate of the second liquid crystal cell (on the alignment film 22a side) is set. And γ
₂₂ is orthogonal.

As shown by arrows P and N in the figure, the first
The twist directions of the second liquid crystal cell are opposite to each other.

Therefore, the photo-writing type LCD of this embodiment
The liquid crystal cell provided in 1 has a structure in which liquid crystal cells having twist angles of 45 ° are laminated with the twist directions being opposite to each other.

The following Table 1 shows an optical writing type LC according to the present invention.
7 is a table comparing the voltage-transmittance characteristics of the liquid crystal cell provided in D with the characteristics of the single-layer liquid crystal cell of the conventional example.

[0034]

[Table 1]

In the table, Δn is the birefringence and d is the thickness of the liquid crystal layer. In addition, α is a parameter representing steepness, the ratio of each voltage when the transmittance is 10% and 90%, γ is the angle between the liquid crystal molecular axis and the incident polarization axis,
As shown in FIG. 1 (B), the rubbing direction γ ₂₁ of the alignment film 22b is
And γ = 0 ° when the incident polarization axes are the same.

In the two-layer cell, α of γ ≠ 0 ° is the angle γ =
Among the cases of + 22.5 ° or −22.5 °, the values corresponding to the steeper case, that is, the case where the change of the transmittance with respect to the change of the voltage is large are shown.

Further, the angle γ is typically represented by + 22.5 ° or −22.5 °, but the twist angle is within the range of γ ± 10 °.
A steeper characteristic than that of a single-layer liquid crystal cell at 45 ° is obtained. That is, the angle between the incident polarization axis and the liquid crystal molecular axis is 2
2.5 ° ± 10 ° is desirable. Also, for comparison,
Table 1 also shows the value of α when γ = 0 °.

FIG. 3 shows an optical writing type LCD according to the present invention.
FIG. 6 is a diagram showing an example in which the voltage-transmittance characteristics of the example of the liquid crystal cell provided in FIG.

As shown in the figure, the single-layer liquid crystal cell with a twist angle of 45 °, which has been conventionally used in the photo-writing type LCD, has a small change in transmittance with respect to a change in voltage. For example, as shown in the column "1 layer cell" in Table 1, when the liquid crystal is ZLI-1646 (manufactured by Merck & Co., Inc.), and the value of α of the liquid crystal cell with a twist angle of 45 ° is 1.42 when Δnd = 0.45. is there.

On the other hand, the impedance of each layer of the photo-writing type LCD of this embodiment is 3.3 × 10 5 when the photoconductive layer is in the dark state.
⁷ ohms (ZPC, d), 2.1 x 10 ⁶ ohms (ZP
C, p), the dielectric mirror and the light-shielding layer together 2.0 × 10 ⁷
Since the ohm (ZM) and the liquid crystal layer are 7.2 × 10 ⁷ ohm (ZLC), from the following equation, {ZLC / (ZPC, p + ZM + ZLC)} / {ZLC / (ZPC, d
+ ZM + ZLC)} = 1.3. If the voltage applied to the liquid crystal layer is 1 in the dark state where the writing light is not radiated, in the bright state where the writing light is radiated
Only a voltage of 1.3 is applied to the liquid crystal layer. Therefore, in the liquid crystal cell having the value of α of 1.42, the transmittance in the bright state was low and the display was dark. In contrast to the conventional one-layer liquid crystal cell having a contrast of 5, according to this embodiment, Δnd = 0.
Comparing the case of 45, as shown in Table 1, since the steepness is improved from 1.42 to 1.26 in α value, a contrast of 10 can be obtained.

Next, the result of projection by the photo-writing type LCD having the liquid crystal cell formed as described above will be described. This projection is performed by using an optical system, which allows the characteristic evaluation of the liquid crystal cell.

FIG. 4 is a schematic configuration diagram showing the configuration of an embodiment of a projection type liquid crystal display device having a photo-writing type LCD according to the present invention.

As shown in the figure, in the projection type liquid crystal display device including the photo-writing type LCD of this embodiment, the light source 41,
An optical system including a diaphragm 42, a lens 43, an interference filter 44, a polarization beam splitter 45, a projection lens 48, a screen 49, an illuminance meter 50, a writing light source 51, a writing pattern 52 and a lens 53, and an optical writing LCD 46 are provided. ing.

The optically writable LCD 46 is arranged in the optical path between the polarization beam splitter 45 and the lens 53, and comprises a first liquid crystal cell 46a to which a voltage is applied and a second liquid crystal cell 46b for compensation. ing. These first liquid crystal cells 46a
The second liquid crystal cell 46b and the second liquid crystal cell 46b respectively correspond to the first liquid crystal cell and the second liquid crystal cell described in FIG.

In such a structure, the writing light source 51
The writing pattern 52 is irradiated with light from the lens 53 through the lens 53, and the image of the writing pattern 52 is displayed on the optical writing LCD 46.
Write to. The light from the light source 41 is reflected by the polarization beam splitter 45 through the diaphragm 42, the lens 43 and the interference filter 44, and then only the p-wave is the optical writing type in which the image of the writing pattern 52 is formed as described above. It is incident on the LCD 46. The polarization state of the incident light is modulated by the change in the orientation of the liquid crystal layer of the photo-writing LCD 46 in the portion corresponding to the written image, and only the s-wave of the modulated light passes through the polarization beam splitter 45 and the projection lens. Projected by 48 onto screen 49.

In this experiment, ZLI-1646 (manufactured by Merck) was used as the liquid crystal, and Δnd of the first liquid crystal cell to which a voltage was applied.
Was set to 0.41 and the value of Δnd of the second liquid crystal cell was set to 0.37. The ON voltage applied to the first liquid crystal cell is 1.24.
(V) and off-voltage were set to 0.95 (V).

FIG. 5 is a diagram showing the result of the voltage- illuminance characteristic measured on the screen 49 of the projection type liquid crystal display device having the photo-writing type LCD according to the present invention, which is applied to the first liquid crystal cell. The illuminance (lux lx) on the screen 49 was measured by the illuminometer 50 while changing the voltage, and the results are shown in Table 2 below.
Shown in

[0048]

[Table 2]

As shown in these figures, γ = −2 with respect to the contrast (CR) 16 obtained when γ = 0 °.
At 2.5 °, a contrast more than twice that of γ = 0 ° was obtained, 34. In the preferred embodiment, the value of .DELTA.nd of the liquid crystal enclosed in the liquid crystal cell to which the voltage is applied is from 0.45.
A value of 0.75 is desirable.

According to this embodiment, an optical writing type LCD
By shifting the angle of the polarization axis incident on the liquid crystal layer from the molecular axis of the liquid crystal, the relationship between the applied voltage and the transmittance of the incident polarized light was measured using the device, and according to the above results, the steepness is improved. That is, the change in the transmittance with respect to the change in the voltage can be increased. Therefore, the optical writing LC
When D is driven at a certain voltage ratio, the sharpness is improved, so that a bright display can be obtained in the ON state.

[0051]

As described above, the present invention is an optical writing type liquid crystal display device having two twisted nematic type liquid crystal cells, and the two liquid crystal cells have a twist angle of 45.
The twisting direction is opposite at 0 °, and the
Between the birefringence of the liquid crystal enclosed in the crystal cell and the thickness of the liquid crystal layer
The product Δnd is between 0.45 and 0.75 and the incident polarization axis is
Opposite to the twist direction of the liquid crystal with respect to the liquid crystal molecular axis on the shooting side
Which is configured to form an angle of 22.5 ° ± 10 ° to the direction, with respect to the change of the voltage at the ON / OFF of the applied voltage
The steepness can be improved by increasing the change in transmittance.
You. Therefore, the photo-writing type liquid crystal display device can be operated at a certain voltage.
When driving at the pressure ratio, the steepness is improved, so in the ON state
The brightness of the display is improved and the contrast is large.
The display can be changed to be easier to see .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a liquid crystal molecule axis of a first and a second liquid crystal cell and an incident polarization axis.

FIG. 2 is a cross-sectional view showing a configuration of an embodiment of a liquid crystal cell provided in the photo-writing type LCD according to the present invention.

FIG. 3 is a diagram showing an example of comparison of voltage-transmittance characteristics between an example of a liquid crystal cell provided in the photo-writing type LCD according to the present invention and a conventional example.

FIG. 4 is a schematic configuration diagram showing a configuration of an embodiment of a projection type liquid crystal display device including an optical writing type LCD according to the present invention.

FIG. 5 is a diagram showing results of voltage- illuminance characteristics measured on a screen of a projection type liquid crystal display device including an optical writing type LCD according to the present invention.

[Explanation of symbols]

 11a, 11b, 21a, 21b Glass substrates 12a, 12b Transparent electrode 13 a-Si layer 14 Light-shielding layer 15 Dielectric mirror 16a, 16b, 22a, 22b Alignment film 17, 23 Seal member 18, 24 Liquid crystal layer 19 AC power supply 25 Resin 46 LCD cell

Claims (1)

(57) [Claims] 1. An optical writing type liquid crystal display device having two twisted nematic type liquid crystal cells, wherein
The liquid crystal cell has a twist angle of 45 ° and the twist direction is opposite.
Liquid that is in the opposite direction and is enclosed in a liquid crystal cell that applies voltage
The product of the birefringence of the crystal and the thickness of the liquid crystal layer Δnd is 0.45 to 0.
75, and the incident polarization axis is aligned with the liquid crystal molecular axis on the light incident side.
Then, in the direction opposite to the twist direction of the liquid crystal, 22.5 ° ± 10 °
An optical writing type liquid crystal display device characterized by being configured to form an angle .